More than 550,000 Israelis have downloaded the Red Alert phone app, says its co-creator, Ari Sprung.

Fifteen to 90 seconds before a rocket flies into Israel, nearly 600,000 people receive the same cellphone notification: "Rockets Attack" it reads, followed by the name of an Israeli city.

Only seconds separate the phone ping from sirens that blare in Israel whenever a rocket is launched from Gaza. But those few seconds are an extra cushion for Israelis who sprint to a bomb shelter to take cover.

More than 550,000 Israelis have downloaded the Red Alert phone app, says its co-creator, Ari Sprung, an Android developer for an Israeli start-up who 12 years ago was a tank commander in Israel's army.

But the app also has become popular among Israel supporters internationally, Sprung said from Jerusalem. It has been downloaded by 50,000 people outside Israel - most of them with relatives in Israel or supporters of Israel who want to follow events in real time.

"Through this app I get constant reminder of what it's like to live under fire," said Rabbi Zalman Tiechtel, director of the Chabad Jewish Centre at the University of Kansas. "This app really helps me live every single day what they are living."

Sprung said he never intended for the tool to be used outside Israel, and the international interest is simply a byproduct of today's interconnected world.

"It's not propaganda," Sprung said. "If you download it, it's annoying. But we had a cry from people who wanted to see what we're going through and show solidarity."

Lucy Kurtzer-Ellenbogen, director of Arab-Israeli programmes at the US Institute of Peace in Washington, said the app's value in Israel is unchallenged. "It definitely provides a peace of mind, and with that you can have a sense of control over the situation," she said. "You can't always hear the sirens."

Sprung won't say from where he receives the Red Alert information, although Israel's military has publicly supported the app.

This article appeared in the South China Morning Post print edition as Red Alert app warns Israelis of attacks